This invention relates to truck scales and more particularly to truck scales which can be transported in foldable sections to a site and then center-locked into position.
Increase in size of trucks and use of strain gauges to replace prior weight measurement devices have been two main factors affecting development of truck scales. Basically, a modern truck scale is a bridge or a series of bridge units suspended on a strain-gauge load cell to measure weight at opposite ends of each bridge unit.
Examples of different but pertinent prior art are described in the following patent documents.
______________________________________ COUNTRY NUMBER DATE NAME ______________________________________ U.S. 4,949,798 Aug. 21, 1990 Strasser, et al. U.S. 4,874,050 Oct. 17, 1989 Strasser, et al. U.S. 4,828,055 May 9, 1989 Hamilton, et al. U.S. 3,935,914 Feb. 3, 1976 Nordstrom, et al. U.S. 3,444,942 May 20, 1969 Murphy ______________________________________
The two Strasser, et al. patents described bridge-support technology applicable particularly to weigh bridges, but did not teach the center-lock features nor the less expensive beam technology employed in the present invention. Rather, the latter patented devices employed means for transmitting load to a load cell that are more difficult to inspect and repair, less reliable and more expensive to construct and assemble than the means employed in this invention. The Hamilton patent taught a bolt linkage system that is very different from a hinge linking mechanism taught by this invention. Hamilton did not have a central locking means taught by this invention to decrease costs of construction and increase portability. The Nordstrom, et al. patent taught a three-point suspension system for measuring what it called "overturning moments" resulting from unbalanced loading of trucks. Murphy taught modular bridges in a plurality of patents, including the one listed. In conclusion, none of the prior patents teach central locking, hinging or load-cell mounting means employed by this invention.
Furthermore, previous truck scales have been anchored at sides and ends by various types of wall structures. Such wall structures are large, expensive and difficult to transport. Some must be built largely on site. Equally important, such truck scales are not reliable because of expansion and contraction due to temperature changes. For instance, making the scales tight enough for hot weather makes them too loose for cold weather. The latter size differential caused by expansion and contraction of metal due to temperature changes results from a relatively long distance between sides and between ends.
Heretofore, advantages of a reliable hinge system for folding bridge units for foldability has not been recognized. Most have been so heavy that sectioning them into pieces has been the main method for achieving portability. Consequently, a rigid type of hinge employed in this invention was not used in the prior art.
Additionally, convenient removal and replacement of load cells to check and adjust them for accuracy as provided by this invention were not available in the prior art, nor was a sturdy and long-lasting attachment means for load cells having these advantages.